Koichi Ogawa

Osaka Prefecture University, Sakai, Ōsaka, Japan

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Publications (65)17.72 Total impact

  • Source
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    ABSTRACT: The relationship between joint strength and deformation heat input at the upset stage and the relationship between joint strength and upset burn-off length were examined on friction welded joints of 1050 pure aluminum to C I 100 tough pitch copper. Joint quality was evaluated from the tensile strength and fatigue strength. It was found that both the deformation heat input at the upset stage and the upset burn-off length correlated well with joint strength. Additionally, when the deformation heat input at the upset stage or upset burn-off length exceeded a certain value, stable tensile strength was obtained. The mixing layer, intermetallic compounds of Al-Cu were interpolated into A 1050, formed at the weld interface, and joints having a thick mixing layer fractured at the weld interface. Joint efficiencies of sound joints for the fatigue limit of the A 1050 base metal were 88-100%. Judging front the fatigue limit, sound joints could be produced when either the deformation heat input at the upset stage or the upset burn-off length exceeded a certain value. [doi: 10.2320/matertrans.L-MRA2008836]
    Journal of Japan Institute of Light Metals 12/2008; 49(12):2786-2791. DOI:10.2320/matertrans.L-MRA2008836
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    ABSTRACT: We have developed digital phantoms to be used for a basic education on an image quality and a quantification of SPECT data. Differing from the digital phantoms developed by Castiglioni and et al, several SPECT projection data sets were generated by Monte Carlo simulations (EGS4 code) with different acquisition parameters. A physical, brain and cardiac phantoms were generated. An external shape of the physical phantom is a 200 mm diameter and 200 mm long cylinder. Three objects, each of which consists of 4 mm, 10 mm, 20 mm, 40 mm and 60 mm diameter rods (each rod is 30 mm long) , are set in. Shapes of the brain phantom were created using a MRI data set. Shapes of the cardiac phantom were created using a CT image set. Tc-99m was used for the simulations. The Monte Carlo simulations were performed, taking account of Compton scattering, photoelectric effect and degradation of a spatial resolution due to collimator aperture. SPECT acquisition parameters were collimator type, pixel length, acquired photon count, projection number and radius of detector rotation. Ideal SPECT projection data and transaxial image were generated as reference (standard) data. Several attenuation maps with different attenuation coefficients can be used for an evaluation of an attenuation correction. The triple energy window setting was used for an evaluation of a scatter correction such as the TEW method. Overall, primary and scattered photons were saved in different files. By using the proposed phantoms, spatial resolution, contrast, signal to noise ratio and quantification with SPECT data acquisition and processing parameters were evaluated. The phantoms are considered to be useful for understanding the fundamental performance on SPECT.
    Nuclear Science Symposium Conference Record, 2007. NSS '07. IEEE; 01/2007
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    ABSTRACT: The purpose of this study is to estimate temperature distribution in the vicinity of weld interface during a friction welding process involving an upset process. On the base of a simple model of friction heat input, a non-steady heat conduction analysis was carried out by finite element method. As a result from a comparison of the estimated temperature distribution with the experimental data, it turned out that the friction heat input model that allowed for the effects of temperature and linear velocity on the friction coefficient was appropriate. This heat input model could simulate adequately the change in friction heat input and temperature distribution in a friction welding process. As a result, the relationship between burn-off length and temperature distribution in upset process has been explained and also the relationship between temperature distribution and width of heat-affected zone has been obtained. This heat input model allows us to estimate temperature distribution in friction welding, from friction pressure, rotation speed and the thermal property of base metal, even where a friction-welding machine does not have a function of torque measurement.
    01/2007; 31(4). DOI:10.7791/jhts.31.225
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    ABSTRACT: An approach to combine a friction heat input model with a non-steady heat conduction analysis has enabled a numerical simulation of a heat input and a transient temperature distribution in friction welding processes. This report describes the result obtained by applying this approach to the friction welding process of two similar materials of S25C carbon steel or SUS304 stainless steel. When base metals are different, the friction heat input model and the thermophysical property data are changed depending on a quality of base metal. Comparison between a calculated result and an experimental result was carried out, and appropriateness of this approach was examined. Furthermore, a difference of temperature distribution in friction welding region with the difference of thermophysical property of base metal was examined, and also the heat-affected zone was investigated. As a result, it was verified that this approach could simulate a characteristic of a welding process in brake-type friction welding. And the calculated results agreed with the experimental results on a difference of quantity of heat input to be caused by a difference of a friction welding condition. A difference of a temperature history caused in a different base metal appeared to be estimated from a calculated result, and it was confirmed that this approach was appropriate. The width of heat-affected zone was estimated by an calculated result of the maximum temperature distribution in the vicinity of friction surface by using this approach combining a friction heat input model with a non-steady heat conduction analysis.
    01/2007; 32(4). DOI:10.7791/jhts.32.236
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    ABSTRACT: The effect of heat input on joint strength in the brake type friction welding has become clear, but the effect in the inertia type friction welding is not clear even at present. Then in this report, inertia type friction welding of 6061 aluminum alloy was carried out in order to examine the effect of unit heat input, burn-off length and burr shape on the joint strength. The heat input (mechanical work) was calculated by burn-off speed and welding pressure in the final stage. The joint strength was examined by tensile test. The final stage (welding time) of inertia type friction welding corresponding to the upset stage of brake type friction welding was searched using the relationship between heat input and joint strength. Using the most proper-final stage obtained, the relationships between unit final deformation heat input and joint strength, final burn-off length and joint strength, and burr shape and final deformation heat input were examined. Also the minimum unit final deformation heat input and minimum final burn-off length required for making a sound joint were also examined. The results showed that within this experiment the most proper-final stage (welding time) was 0.1s, and the limit unit final deformation heat input and limit final burn-off length were 19J/s and 0.3mm, respectively.
    01/2007; 32(2). DOI:10.7791/jhts.32.145
  • Kazuhiko Kowase, Koichi Ogawa
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    ABSTRACT: In a conventional X-ray CT scanner with Gd<sub>2</sub>O<sub>2</sub>S detectors, the measured data are the whole X-ray energy deposited to each detector bin. The detection of energy is performed in an integration manner, so that the contribution of photons having low energy is smaller than that of those having high energy. But if we use a semiconductor detector such as CdTe with a photon counting mode, we may obtain valuable information for the medium being imaged. For example, if we obtain some information about energy spectra for detected photons, we can enhance the contrast resolution of media having almost the same linear attenuation coefficient as soft tissues by weighing the counted photons having lower energy. To clarify the validity of our proposed method, we used a CdTe semiconductor detector and reconstructed images with projection data measured with different thresholds in counting X-ray photons.
    Nuclear Science Symposium Conference Record, 2006. IEEE; 12/2006
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    ABSTRACT: In an X-ray CT system the energy fluence of X-rays is commonly measured with scintillation detectors in the data acquisition. To enhance the contrast in low contrast media we proposed a new concept of X-ray CT system. This technique utilized the information for an energy spectrum of X-rays. That is, we applied more than two voltages to an X-ray tube and obtained data measured with different energy spectra. Without increasing the irradiation dosage of X-rays, the contrast enhancement was carried out with arithmetic between these reconstructed images. The aim of this study is to clarify the validity of such an energy-modulated X-ray CT with simulations.
    Nuclear Science Symposium Conference Record, 2006. IEEE; 12/2006
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    ABSTRACT: A CdZnTe semiconductor detector, which works at room temperature, may realize a next generation gamma-camera system due to its high spatial resolution and high energy resolution. We made a prototype gamma-camera system with CdZnTe detectors to evaluate the feasibility of the semiconductor gamma-camera. This paper described our prototype system and some results obtained with this system.
    Nuclear Science Symposium Conference Record, 2006. IEEE; 12/2006
  • Takashi KURIHARA, Koichi Ogawa
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    ABSTRACT: In a simulation study the description of an object is very important for high speed calculation in photon transportation with a Monte Carlo method. For this object description we developed a maximum rectangular region (MRR) method in 2000 (TNS vol.47, No.3) thereby reducing the calculation time. In this paper we proposed a more efficient method in which we considered the location of a photon within a rectangular region. This method could reduce the calculation time as compared with the MRR method.
    01/2006; DOI:10.1109/NSSMIC.2006.354309
  • Journal of Japan Institute of Light Metals 01/2006; 56(1):2-7. DOI:10.2464/jilm.56.2
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    ABSTRACT: The Ono's rotary bending fatigue test and the cantilever rotary bending fatigue test were carried out on friction-welded 6061 aluminum alloy joints, and the relationship between the deformation heat input in the upset stage or the upset burn-off length and fatigue strength was examined. In the Ono's type test, sound joints, which fractured in the heat affected zone in the tensile test, fractured in the heat affected zone also and the fatigue limit of these joints was slightly lower than that of 6061 aluminum alloy base metal. This is because joints fractured in the softened area in both tensile test and Ono's type test using smoothed test specimens. While, in the cantilever type test, the fatigue limit of sound joints was a little more than or a little less than that of 6061 aluminum alloy base metal. It seems that a weld and a structure at the weld interface affected fatigue strength in the cantilever type test using notched test specimens. Judging from the fatigue limit obtained, sound joints could be produced when either the deformation heat input in the upset stage or the upset burn-off length exceeded a certain value.
    Journal of Japan Institute of Light Metals 01/2006; 56(7):366-370. DOI:10.2464/jilm.56.366
  • Journal of the Society of Materials Science Japan 01/2004; 53(5):512-517. DOI:10.2472/jsms.53.512
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    ABSTRACT: In order to measure the heat input (quantity of heat) generated during friction welding, a new type calorimeter of acryl resin was developed, and applied to friction welding of a stainless steel. The heat input measured during friction welding was in good agreement with the values calculated from the measured values of friction torque, burn-off length, rotation speed and pressure. Being classified into friction and deformation heat inputs, the friction heat input was much greater than the deformation heat input through the friction and upset stages.
    01/2004; 30(5). DOI:10.7791/jhts.30.279
  • Journal of the Society of Materials Science Japan 01/2004; 53(5):532-538. DOI:10.2472/jsms.53.532
  • Source
    Jianbin Ju, Yasuo Suga, Koichi Ogawa
  • Journal of Japan Institute of Light Metals 01/2003; 53(2):43-49. DOI:10.2464/jilm.53.43
  • QUARTERLY JOURNAL OF THE JAPAN WELDING SOCIETY 01/2003; 21(3):381-388. DOI:10.2207/qjjws.21.381
  • Materials Science Forum 01/2003; DOI:10.4028/www.scientific.net/MSF.426-432.4471
  • Materials Science Forum 01/2002; DOI:10.4028/www.scientific.net/MSF.396-402.1525
  • Materials Science Forum 01/2002; 396-402(9):1685-1690. DOI:10.4028/www.scientific.net/MSF.396-402.1685

Publication Stats

119 Citations
17.72 Total Impact Points

Institutions

  • 1992–2008
    • Osaka Prefecture University
      • Faculty of Liberal Arts and Sciences
      Sakai, Ōsaka, Japan
  • 1996–1998
    • Hosei University
      • Department of Electronics and Electrical Engineering
      Edo, Tōkyō, Japan
  • 1991
    • Keio University
      • Department of Radiology
      Tokyo, Tokyo-to, Japan